This invention relates to a chair base having improved manufacturability and reduced cost, particularly with respect to the caster pintle mount provided adjacent the ends of the base legs.
Chairs as typically used in offices and the like often include bases having radially extending legs with casters at their ends for movably supporting the chair. To provide the necessary strength and durability, it is conventional to form a unitary base member constructed of steel, with a plurality of legs (typically five) disposed angularly around and radiating outwardly from a center hub. The inner ends of the legs are typically welded to the hub, and the outer ends of the legs are typically provided with a support sleeve associated therewith for retention of the caster pintle. In recent years it has been a common practice to form the individual legs from a flat platelike steel blank which is deformed to define an elongate tubular construction, whereby one end thereof is welded to the center hub, and the other end is subjected to suitable manufacturing processes so as to permit a separate pintle-accommodating support sleeve to be fixedly secured thereto, such as by welding. Alternatively, in some applications the caster pintle is accommodated in openings formed in the leg member and is then directly welded to the base member. In most applications, the unitary steel base member is thereafter provided with a cover disposed thereover to provide the base assembly with desired aesthetics. While a base assembly of the above type, and specifically a unitary steel base member of the above construction provides desirable strength and durability, nevertheless the overall manufacture thereof is relatively complex and costly due to the numerous parts and forming steps associated therewith.
Accordingly, it is an object of this invention to provide an improved chair base, specifically a unitary steel base member which improves on both the construction of the base and the manufacturing process thereof so as to result in a base which possesses desired strength and durability but which can be manufactured utilizing fewer parts and which permits manufacture to be carried out more efficiently so that the overall base member is less costly.
According to the present invention, the individual leg of the base member is defined by an elongate tubular member which adjacent one end thereof is provided with upper and lower sleevelike hubs which are integrally and monolithically joined to the respective upper and lower walls of the leg member and which project coaxially inwardly of the leg member toward one another. These coaxially aligned hubs define an opening, preferably a cylindrical opening, which extends vertically through the leg member and permits the pintle of a caster to be snugly and durably supported therein, whereby provision of a separate pintle-retaining sleeve is not required.
In the improved base member of this invention, as aforesaid, the upper and lower walls of the leg member are initially provided with small pilot openings formed therethrough, which openings are of smaller cross section than the caster pintle. The wall material surrounding the pilot openings is then physically deformed (extruded) transversely into the interior of the leg member, such as by an extruding tool, and is reshaped into an annular sleevelike hub which projects generally transversely from the respective wall through a selected distance into the interior of the leg member. The annular hubs as deformed from the upper and lower walls are disposed in coaxially aligned and opposed relationship to define a pintle-accommodating opening which extends vertically through the leg member.
According to the present invention, the manufacturing process for the leg member of the unitary base includes the steps of forming small pilot holes through the top and bottom walls of the leg member, and reshaping the annular wall material surrounding each preformed pilot opening so as to result in formation of an annular pintle-accommodating hub which is integrally and monolithically joined to and projects inwardly from the respective top and bottom wall, whereby the pintle-accommodating hubs define therein a cross sectional opening which is greater in size than the respective pilot opening as originally formed in the respective top and bottom wall. The aforementioned manufacturing process can be carried out by a first tool which forms the pilot opening followed by application of a second tool which extrudes the surrounding annular wall so as to define the hub. In the alternative, the process can be carried out by a single tool which initially preforms the pilot opening and thereafter immediately follows up with the extrusion of the annular wall portion so as to permit formation of the annular pintle-accommodating hub.